This invention relates to foamable polymer compositions comprising a1) a substantially random interpolymer produced from i) one or more xcex1-olefin monomers and ii) one or more vinyl or vinylidene aromatic monomers and/or one or more sterically hindered aliphatic or cycloaliphatic vinyl or vinylidene monomers, and optionally iii) other polymerizable ethylenically unsaturated monomer(s), or a2) an interpolymer comprising polymerized units of ethylene and vinyl acetate or a3) a combination of the polymers a1) and a2) and a high molecular weight polysiloxane.
Foamable compositions comprising ethylene/vinyl acetate polymers are well known and widely used for making footwear, such as shoe soles. Substantially random interpolymers a1) and their use for producing foams are described in U.S. Pat. No. 5,460,818. From such polymers, foamed articles can be produced which are generally soft, flexible and resilient. They can also be hard, that means less resilient and less flexible, and exhibit high compression set. Accordingly, the above-mentioned interpolymers can be potentially used in many applications, such as tarps, coated fabrics, shoe soles, shoe stiffeners, and artificial leather, tires for bicycles, wheel chairs, and stroller wheels, and in wire and cable insulation and jacketing formed by general extrusion or by calendered sheets or films with and without fillers. Some of the shoe soles and wheels are produced via injection molding and cross-linking processes where usually ethylene/vinyl acetate polymers are hard to control since they tend to stick to molds and to expand unevenly.
For many of these applications, such as shoe soles, wheels and wire and cable insulation, it is important that the flexible articles also have a good surface abrasion resistance. In some applications like shoe soles, a high coefficient of friction (COF) is also desirable. An unduly low coefficient of friction increases the danger of slipping on the ground.
Accordingly, one object of the present invention is to improve the surface abrasion resistance of foams comprising the above-mentioned interpolymers. A preferred object of the present invention is to improve the surface abrasion resistance of such foams without decreasing their coefficient of friction.
One aspect of the present invention is a foamable polymer composition which comprises
a1) a substantially random interpolymer produced from i) one or more xcex1-olefin monomers and ii) one or more vinyl or vinylidene aromatic monomers and/or one or more sterically hindered aliphatic or cycloaliphatic vinyl or vinylidene monomers, and optionally iii) other polymerizable ethylenically unsaturated monomer(s), or
a2) an interpolymer comprising polymerized units of ethylene and vinyl acetate or
a3) a combination of the polymers a1) and a2); and
b) a polydiorganosiloxane having a viscosity of at least one million centistoke at 25xc2x0 C.; and
c) a foaming agent.
Another aspect of the present invention is a foam comprising
a1) a substantially random interpolymer produced from i) one or more xcex1-olefin monomers and ii) one or more vinyl or vinylidene aromatic monomers and/or one or more stenically hindered aliphatic or cycloaliphatic vinyl or vinylidene monomers, and optionally iii) other polymerizable ethylenically unsaturated monomer(s), or
a2) an interpolymer comprising polymerized units of ethylene and vinyl acetate or
a3) a combination of the polymers a1) and a2); and
b) a polydiorganosiloxane having a viscosity of at least one million centistoke at 25xc2x0 C.
Yet another aspect of the present invention is a process for producing a foam wherein the above-mentioned foamable polymer composition is exposed to an elevated temperature to release blowing agent and to form a foam structure.
Yet another aspect of the present invention is a fabricated article comprising the above-mentioned foam.
Yet another aspect of the present invention is a method of improving the abrasion resistance of a foam comprising:
a1) a substantially random interpolymer produced from i) one or more xcex1-olefin monomers and ii) one or more vinyl or vinylidene aromatic monomers and/or one or more sterically hindered aliphatic or cycloaliphatic vinyl or vinylidene monomers, and optionally iii) other polymerizable ethylenically unsaturated monomer(s), or
a2) an interpolymer comprising polymerized units of ethylene and vinyl acetate or
a3) a combination of the polymers a1) and a2); which method comprises the step of incorporating into said foam an effective amount of a polydiorganosiloxane having a viscosity of at least one million centistoke at 25xc2x0 C.
The term xe2x80x9ccomprisingxe2x80x9d as used herein means xe2x80x9cincludingxe2x80x9d. The term xe2x80x9ccomprisingxe2x80x9d is not to be understood to mean xe2x80x9cconsisting ofxe2x80x9d.
The term xe2x80x9cinterpolymerxe2x80x9d is used herein to indicate a polymer wherein at least two different monomers are polymerized to make the interpolymer.
The term xe2x80x9csubstantially randomxe2x80x9d in the substantially random interpolymer resulting from polymerizing i) one or more xcex1-olefin monomers and ii) one or more vinyl or vinylidene aromatic monomers and/or one or more sterically hindered aliphatic or cycloaliphatic vinyl or vinylidene monomers, and optionally iii) other polymerizable ethylenically unsaturated monomer(s) as used herein generally means that the distribution of the monomers of said interpolymer can be described by the Bernoulli statistical model or by a first or second order Markovian statistical model, as described by J. C. Randall in POLYMER SEQUENCE DETERMINATION, Carbon-13 NMR Method, Academic Press New York, 1977, pp. 71-78. Preferably, the substantially random interpolymer resulting from polymerizing one or more xcex1-olefin monomers and one or more vinyl or vinylidene aromatic monomers, and optionally other polymerizable ethylenically unsaturated monomer(s), does not contain more than 15 percent of the total amount of vinyl or vinylidene aromatic monomer in blocks of vinyl or vinylidene aromatic monomer of more than 3 units. More preferably, the interpolymer is not characterized by a high degree of either isotacticity or syndiotacticity. This means that in the carbon-13 NMR spectrum of the substantially random interpolymer the peak areas corresponding to the main chain methylene and methine carbons representing either meso diad sequences or racemic diad sequences should not exceed 75 percent of the total peak area of the main chain methylene and methine carbons. By the subsequently used term xe2x80x9csubstantially random interpolymerxe2x80x9d is meant a substantially random interpolymer produced from the above-mentioned monomers.
Suitable xcex1-olefin monomers which are useful for preparing the substantially random interpolymer include, for example, xcex1-olefin monomers containing from 2 to about 20, preferably from 2 to about 12, more preferably from 2 to about 8 carbon atoms. Particularly suitable are ethylene, propylene, butene-1,4-methyl-1-pentene, hexene-1 or octene-1 or ethylene in combination with one or more of propylene, butene-1,4-methyl-1-pentene, hexene-1 or octene-1. Most preferred are ethylene or a combination of ethylene with C3-8-xcex1-olefins. These xcex1-olefins do not contain an aromatic moiety.
Optional other polymerizable ethylenically unsaturated monomer(s) include strained ring olefins such as norbornene and C1-10 alkyl or C6-10 aryl substituted norbornenes, with an exemplary interpolymer being ethylene/styrene/norbornene.
Suitable vinyl or vinylidene aromatic monomers which can be employed to prepare the substantially random interpolymer include, for example, those represented by the following Formula I 
wherein R1 is selected from the group of radicals consisting of hydrogen and alkyl radicals containing from 1 to about 4 carbon atoms, preferably hydrogen or methyl; each R2 is independently selected from the group of radicals consisting of hydrogen and alkyl radicals containing from 1 to about 4 carbon atoms, preferably hydrogen or methyl; Ar is a phenyl group or a phenyl group substituted with from 1 to 5 substituents selected from halo, Cl4-alkyl, and C1-4-haloalkyl; and n has a value from zero to about 4, preferably from zero to 2, most preferably zero. Particularly suitable monomers include styrene and lower alkyl- or halogen-substituted derivatives thereof. Preferred monomers include styrene, xcex1-methyl styrene, the lower alkyl-(C1-C4) or phenyl-ring substituted derivatives of styrene, such as for example, ortho-, meta-, and para-methylstyrene, t-butyl styrene, the ring halogenated styrenes, such as chlorostyrene, para-vinyl toluene or mixtures thereof. A more preferred aromatic monovinyl monomer is styrene.
By the term xe2x80x9csterically hindered aliphatic or cycloaliphatic vinyl or vinylidene monomersxe2x80x9d, it is generally meant the addition of polymerizable vinyl or vinylidene monomers corresponding to Formula II 
wherein A1 is a sterically bulky, aliphatic or cycloaliphatic substituent of up to 20 carbons, R1 is selected from the group of radicals consisting of hydrogen and alkyl radicals containing from 1 to about 4 carbon atoms, preferably hydrogen or methyl; each R2 is independently hydrogen or an alkyl radical containing from 1 to about 4 carbon atoms, preferably hydrogen or methyl; or alternatively R1 and A1 together form a ring system. By the term xe2x80x9csterically bulkyxe2x80x9d is meant that the monomer bearing this substituent is normally incapable of addition polymerization by standard Ziegler-Natta polymerization catalysts at a rate comparable with ethylene polymerizations. xcex1-Olefin monomers containing from 2 to about 20 carbon atoms and having a linear aliphatic structure, such as propylene, butene-1, hexene-1 and octene-1, are not considered as sterically hindered aliphatic monomers. Preferred sterically hindered aliphatic or cycloaliphatic vinyl or vinylidene compounds are monomers in which one of the carbon atoms bearing ethylenic unsaturation is tertiary or quaternary substituted. Examples of such substituents include cyclic aliphatic groups such as cyclohexyl, cyclohexenyl, cyclooctenyl, or ring alkyl- or aryl-substituted derivatives thereof, tert-butyl or norbornyl. Most preferred sterically hindered aliphatic or cycloaliphatic vinyl or vinylidene compounds are the various isomeric vinyl-ring substituted derivatives of cyclohexene and substituted cyclohexenes, and 5-ethylidene-2-norbornene. Especially suitable are 1-, 3-, and 4-vinylcyclohexene.
If the substantially random interpolymer contains a vinyl or vinylidene aromatic monomer and a sterically hindered aliphatic or cycloaliphatic monomer in polymerized form, the weight ratios between these two monomer types is generally not critical. Preferably, the substantially random interpolymer contains either a1) one or more vinyl or vinylidene aromatic monomers or b) one or more sterically hindered aliphatic or cycloaliphatic monomers. Vinyl or vinylidene aromatic monomers are preferred over sterically hindered aliphatic or cycloaliphatic monomers.
The preferred substantially random interpolymers are the so-called pseudo-random interpolymers as described in EP-A-0,416,815 by James C. Stevens et al. and U.S. Pat. No. 5,703,187 by Francis J. Timmers, both of which are incorporated herein by reference in their entirety.
The most preferred substantially random interpolymers are interpolymers of ethylene and styrene and interpolymers of ethylene, styrene and at least one xcex1-olefin containing from 3 to 8 carbon atoms.
The substantially random interpolymers usually contain from about 35 to about 99.5, preferably from about 45 to about 99, more preferably from about 50 to about 98 mole percent of at least one aliphatic xcex1-olefin and from about 0.5 to about 65, preferably from about 1 to about 55, more preferably from about 2 to about 50 mole percent of at least one vinyl or vinylidene aromatic monomer and/or sterically hindered aliphatic or cycloaliphatic vinyl or vinylidene monomer. The percentage of the vinyl or vinylidene aromatic monomer and/or sterically hindered aliphatic or cycloaliphatic vinyl or vinylidene monomer can be determined by NMR.
The substantially random interpolymers usually contain from 0 to about 20 mole percent of other polymerizable ethylenically unsaturated monomer(s).
The melt index 12 according to ASTM D 1238 Procedure A, condition E, generally is from about 0.01 to about 50 g/10 minutes, preferably from about 0.01 to about 20 g/10 minutes, more preferably from about 0.1 to about 10 g/10 minutes, and most preferably from about 0.5 to about 5 g/10 minutes. The glass transition temperature (Tg) of the substantially random interpolymers is preferably from about xe2x88x9240xc2x0 C. to about +35xc2x0 C., preferably from about 0xc2x0 C. to about +30xc2x0 C., most preferably from about +10xc2x0 C. to about +25xc2x0 C., measured according to differential mechanical scanning (DMS). The density of the substantially random interpolymer is generally about 0.930 g/cm3 or more, preferably from about 0.930 to about 1.045 g/cm3, more preferably from about 0.930 to about 1.040 g/cm3, most preferably from about 0.930 to about 1.030 g/cm3. The molecular weight distribution, Mw/Ma is generally from about 1.5 to about 20, preferably from about 1.8 to about 10, more preferably from about 2 to about 5.
While preparing the substantially random interpolymer, an amount of atactic vinyl or vinylidene aromatic homopolymer may be formed due to homopolymerization of the vinyl or vinylidene aromatic monomer at elevated temperatures. The presence of vinyl or vinylidene aromatic homopolymer is in general not detrimental for the purposes of the present invention and can be tolerated. The vinyl or vinylidene aromatic homopolymer may be separated from the substantially random interpolymer, if desired, by extraction techniques such as selective precipitation from solution with a nonsolvent for either the substantially random interpolymer or the vinyl or vinylidene aromatic homopolymer. For the purpose of the present invention it is preferred that no more than 30 weight percent, preferably less than 20 weight percent, most preferably less than 10 weight percent, based on the total weight of the substantially random interpolymers of atactic vinyl or vinylidene aromatic homopolymer is present.
The substantially random interpolymer may be modified by typical grafting, hydrogenation, functionalizing, or other reactions well known to those skilled in the art. The polymer may be readily sulfonated or chlorinated to provide functionalized derivatives according to established techniques. The substantially random interpolymer may also be modified by various chain extending or cross-linking processes including, but not limited to peroxide-, silane-, sulfur-, radiation-, or azide-based cure systems. A full description of the various cross-linking technologies is described in U.S. Pat. No. 5,869,591 and EP-A-778,852, the entire contents of both of which are herein incorporated by reference. Dual cure systems, which use a combination of heat, moisture cure, and radiation steps, may be effectively employed. Dual cure systems are disclosed and claimed in EP-A-852,596, incorporated herein by reference. For instance, it may be desirable to employ peroxide crosslinking agents in conjunction with silane crosslinking agents, peroxide crosslinking agents in conjunction with radiation, and sulfur-containing crosslinking agents in conjunction with silane crosslinking agents. The substantially random interpolymer may also be modified by various cross-linking processes including, but not limited to the incorporation of a diene component as a termonomer in its preparation and subsequent cross-linking by the aforementioned methods and further methods including vulcanization via the vinyl group using sulfur for example as the cross linking agent.
A preferred method of preparation of the substantially random interpolymer includes polymerizing a mixture of polymerizable monomers in the presence of one or more metallocene or constrained geometry catalysts in combination with various cocatalysts, as described in EP-A-0,416,815 by James C. Stevens et al. and U.S. Pat. No. 5,703,187 by Francis J. Timmers, both of which are incorporated herein by reference in their entirety. Preferred operating conditions for such polymerization reactions are pressures from atmospheric up to 3000 atmospheres and temperatures from xe2x88x9230xc2x0 C. to 200xc2x0 C. Polymerizations and unreacted monomer removal at temperatures above the autopolymerization temperature of the respective monomers may result in formation of some amounts of homopolymer polymerization products resulting from free radical polymerization.
Examples of suitable catalysts and methods for preparing the substantially random interpolymer are disclosed in EP-A-514,828; as well as U.S. Pat. Nos. 5,055,438; 5,057,475; 5,096,867; 5,064,802; 5,132,380; 5,189,192; 5,321,106; 5,347,024; 5,350,723; 5,374,696; 5,399,635; 5,470,993; 5,703,187; and 5,721,185 all of which patents and applications are incorporated herein by reference.
The substantially random xcex1-olefin/vinyl(idene) aromatic interpolymer can also be prepared by the methods described in JP 07/278,230 employing compounds shown by the general Formula III 
where Cp1 and Cp2 are cyclopentadienyl groups, indenyl groups, fluorenyl groups, or substituents of these, independently of each other; R1 and R2 are hydrogen atoms, halogen atoms, hydrocarbon groups with carbon numbers of 1 to 12, alkoxyl groups, or aryloxyl groups, independently of each other; M is a group IV metal, preferably Zr or Hf, most preferably Zr; and R3 is an alkylene group or silanediyl group used to cross-link Cp1 and Cp2.
The substantially random xcex1-olefin/vinyl(idene) aromatic interpolymer can also be prepared by the methods described by John G. Bradfute et al. (W.R. Grace and Co.) in WO 95/32095; by R. B. Pannell (Exxon Chemical Patents, Inc.) in WO 94/00500; and in Plastics Technology, page 25 (September 1992).
Also suitable are the substantially random interpolymers which comprise at least one xcex1-olefin/vinyl aromatic/vinyl aromatic/xcex1-olefin tetrad disclosed in WO-98/09999-A by Francis J. Timmers et al. These interpolymers can be prepared by conducting the polymerization at temperatures of from about xe2x88x9230xc2x0 C. to about 250xc2x0 C. in the presence of catalysts as those disclosed in WO-98/09999-A. Particularly preferred catalysts include, for example, racemic-(dimethylsilanediyl)-bis-(2-methyl-4-phenylindenyl)zirconium dichloride, racemic-(dimethylsilanediyl)-bis-(2-methyl-4-phenylindenyl)zirconium 1,4diphenyl-1,3-butadiene, racemic-(dimethylsilanediyl)-bis-(2-methyl-4-phenylindenyl)zirconium di-C1-4 alkyl, racemic-(dimethylsilanediyl)-bis-(2-methyl-4-phenylindenyl)zirconium di-C1-4 alkoxide, or any combination thereof. It is also possible to use the following titanium-based constrained geometry catalysts, [N-(1,1-dimethylethyl)-1,1-dimethyl-1-[(1,2,3,4,5-h)-1,5,6,7-tetrahydro-s-indacen-1-yl]silanaminato(2-)-N]titanium dimethyl; (1-indenyl)(tert-butylamido)dimethyl-silane titanium dimethyl; ((3-tert-butyl)(1,2,3,4,5-h)-1-indenyl)(tert-butylamido) dimethylsilane titanium dimethyl; and ((3-isopropyl)(1,2,3,4,5-h)-1-indenyl)(tert-butyl amido)dimethylsilane titanium dimethyl, or any combination thereof.
Further preparative methods for the substantially random interpolymers used in the present invention have been described in the literature. Longo and Grassi (Makromol. Chem., Volume 191, pages 2387 to 2396 [1990]) and D""Anniello et al. (Journal of Applied Polymer Science, Volume 58, pages 1701 to 1706 [1995]) reported the use of a catalytic system based on methylalumoxane (MAO) and cyclopentadienyltitanium trichloride (CpTiCl3) to prepare an ethylene-styrene copolymer. Xu and Lin (Polymer Preprints, Am.Chem.Soc., Div.Polym.Chem., volume 35, pages 686, 687 [1994]) have reported copolymerization using a MgCl2/TiCl4/NdCl3/Al(iBu)3 catalyst to give random copolymers of styrene and propylene. Lu et al. (Journal of Applied Polymer Science, volume 53, pages 1453 to 1460 [1994]) have described the copolymerization of ethylene and styrene using a TiCl4/NdCl3/MgCl2/Al(Et)3 catalyst. Sernetz and Mulhaupt, (Macromol. Chem. Phys., volume 197, pages 1071 to 1083 [1997]) have described the influence of polymerization conditions on the copolymerization of styrene with ethylene using Me2Si(Me4Cp)(N-tert-butyl)TiCl2/methylaluminoxane Ziegler-Natta catalysts. Copolymers of ethylene and styrene produced by bridged metallocene catalysts have been described by Arai, Toshiaki and Suzuki (Polymer Preprints, Am. Chem. Soc., Div. Polym. Chem. Volume 38, pages 349, 350 [1997], U.S. Pat. No. 5,883,213 and DE 197 11 339 A1) and in U.S. Pat. No. 5,652,315, issued to Mitsui Toatsu Chemicals, Inc. The manufacture of o-olefin/vinyl aromatic monomer interpolymers such as propylene/styrene and butene/styrene are described in U.S. Pat. No. 5,244,996, issued to Mitsui Petrochemical Industries Ltd. or U.S. Pat. No. 5,652,315 also issued to Mitsui Petrochemical Industries Ltd. or as disclosed in DE 197 11 339 A1 to Denki Kagaku Kogyo KK. All the above methods disclosed for preparing the substantially random interpolymer are incorporated herein by reference. The polymer composition of the present invention may contain one or more types of substantially random interpolymers a1).
The substantially random interpolymer a1) can be partially or fully replaced by an interpolymer a2) comprising polymerized units of ethylene and vinyl acetate. The interpolymer a2) preferably comprises from 4 to 40 weight percent, more preferably from 12 to 35 weight percent, most preferably from 15 to 30 weight percent, of vinyl acetate units and from 60 to 96 weight percent, more preferably from 88 to 65 weight percent, most preferably from 85 to 70 weight percent of ethylene units. The melt index 12 according to ASTM D 1238 Procedure A, condition E, of the interpolymer a2) preferably is from 0.05 to 100 g/10 min., more preferably from 0.1 to 60 g/10 min., most preferably from 0.5 to 10 g/10 min. The interpolymer a2) comprising polymerized units of ethylene and vinyl acetate may be grafted. In the preferred embodiment of the present invention, the interpolymer a2) is not grafted.
If both interpolymers a1) and a2) are incorporated in the foamable polymer composition of the present invention, their amounts preferably are from 15 to 85, more preferably from 25 to 75, most preferably from 40 to 60 weight percent of the substantially random interpolymer a1), and from 85 to 15, preferably from 75 to 25, most preferably from 60 to 40 weight percent of the interpolymer a2), the weight percentages being based on the total weight of the interpolymers a1) and a2).
The foamable polymer composition of the present invention preferably comprises from about 0.01 to about 20 weight percent, more preferably from about 0.1 to about 10 weight percent, and most preferably from about 0.5 to about 5 weight percent of one or more polydiorganosiloxanes b), based on the total weight of the polymers in the composition. The polydiorganosiloxane b) has a viscosity of at least one million centistoke (mm2/sec.), generally at least 2 millions centistoke, preferably at least 5 millions centistoke, more preferably at least 10 millions centistoke and most preferably at least 15 millions centistoke, measured at 25xc2x0 C. The upper viscosity limit is not critical. The viscosity is generally up to 50 millions centistoke, preferably up to 40 millions centistoke, more preferably up to 30 millions centistoke, most preferably up to 25 millions centistoke, measured at 25xc2x0 C. If the polydiorganosiloxane b) has a viscosity of less than one million centistoke, measured at 25xc2x0 C., the coefficient of friction of the polymer composition is reduced. The consistency of the polydiorganosiloxane b) should preferably be that of a gum.
The organic groups in the polydiorganosiloxanes are independently selected from hydrocarbon or halogenated hydrocarbon groups such as alkyl and substituted alkyl groups containing from 1 to 20 carbon atoms; or alkenyl groups, such as vinyl and 5-hexenyl; cycloalkyl groups, such as cyclohexyl; and aromatic hydrocarbon groups, such as phenyl, benzyl and tolyl. Preferred organic groups are lower alkyl groups containing from 1 to 4 carbon atoms, phenyl, and halogen-substituted alkyl such as 3,3,3-trifluoropropyl. Thus, the polydiorganosiloxane can be a homopolymer, a copolymer or a terpolymer containing such organic groups. Preferred polydiorganosiloxanes include polydimethylsiloxane homopolymers, copolymers consisting essentially of dimethylsiloxane units and methylphenylsiloxane units, copolymers consisting essentially of diphenylsiloxane units and methylphenylsiloxane units, and homopolymers of methylphenylsiloxane units. The polymer composition of the present invention may contain one or more types of polydiorganosiloxanes b).
The polydiorganosiloxane b) generally contains at least one, preferably two or more hydroxyl groups, amine groups or vinyl groups. Most preferred are the hydroxyl groups or vinyl groups. These groups may be located at the ends of the molecule or they may be distributed along the chain or they may be located both at the ends as well as along the chain. Preferably these groups reside at the molecular chain ends, as in the case of hydroxyl, in the form of diorganohydroxysiloxy groups, such as dimethylhydroxysiloxy, diphenylhydroxysiloxy or methylphenylhydroxysiloxy. When the hydroxyl groups, amine groups or vinyl groups are located only along the chain, the terminal groups of the polydiorganosiloxane may be any non-reactive moiety, typically a di- or triorganosiloxy species, such as dimethylvinylsiloxy or trimethylsiloxy. The polydiorganosiloxane b) is preferably a linear polydimethylsiloxane containing up to about 50 mole percent of phenyl units. Most preferably, it is a polydimethylsiloxane homopolymer having dimethylhydroxysiloxy end groups. The polydiorganosiloxanes b) are well known in the art, and many such homopolymers and copolymers are commercially available, for example from Dow Corning. The polydiorganosiloxanes b) are for example described in U.S. Pat. Nos. 5,708,084, 5,916,952 and 6,013,217.
The polydiorganosiloxanes b) do not include the lower molecular weight materials, such as SFR-100 Silicone, available from General Electric Company, which are usually referred to as silicones or silicone oils. These lower molecular weight materials generally have viscosities of less than 1,000 centistoke (mm2/sec.) at 25xc2x0 C. and are used as mold release agents or have viscosities ranging from 10,000 centistoke to 60,000 centistoke (mm2/sec.) at 25xc2x0 C. and are used as internal additives in thermoplastic polymers to give processing advantages and surface property, such as reduced coefficient of friction, improved abrasion resistance, lower wear rates, mold release or faster mold cycles. These materials of lower viscosity have to be distinguished from the described polydiorganosiloxanes b) of higher viscosity that are usually referred to as polydiorganosiloxanes gums.
Furthermore, the foamable polymer composition of the present invention may comprise up to about 70 weight percent, preferably up to about 50 weight percent, more preferably up to about 35 weight percent, of one or more polymeric components other than interpolymers a1) and/or a2), based on the total weight of the polymers in the composition. These polymeric components may be added to modify the properties of the foams of the present invention, such as to improve the tear resistance, to increase the compression set properties at very low foam density, or to modify the tensile strength or modulus of the foam.
Preferred additional, optional polymers are monovinyl or monovinylidene aromatic polymers or styrenic block copolymers or homopolymers or interpolymers of aliphatic xcex1-olefins having from 2 to 20 carbon atoms or xcex1-olefins having from 2 to 20 carbon atoms and containing polar groups.
Suitable monovinyl or monovinylidene aromatic polymers include homopolymers or interpolymers of one or more monovinyl or monovinylidene aromatic monomers, or interpolymers of one or more monovinyl or monovinylidene aromatic monomers and one or more monomers interpolymerizable there with other than an aliphatic xcex1-olefin. Suitable monovinyl or monovinylidene aromatic monomers are represented by the following formula: 
wherein R1 and Ar have the meanings stated in formula I further above. Exemplary monovinyl or monovinylidene aromatic monomers are those listed under formula I further above, particularly styrene. Preferred is high impact polystyrene (HIPS).
Examples of suitable interpolymerizable comonomers other than a monovinyl or monovinylidene aromatic monomer include, for example, C4-C6 conjugated dienes, especially butadiene or isoprene. In some cases, it is also desirable to copolymerize a cross-linking monomer such as a divinyl benzene into the monovinyl or monovinylidene aromatic polymer. Preferred are styrene-butadiene rubbers (SBR), such as high styrene SBR, which is for example available under the trademark Pliolite from Goodyear.
The polymers of monovinyl or monovinylidene aromatic monomers with other interpolymerizable comonomers preferably contain, polymerized therein, at least 50 percent by weight and, preferably, at least 90 percent by weight of one or more monovinyl or monovinylidene aromatic monomers.
Styrenic block polymers are also useful as an additional, optional polymer in the polymeric layer (B). The term xe2x80x9cblock copolymerxe2x80x9d is used herein to mean elastomers having at least one block segment of a hard polymer unit and at least one block segment of a rubber monomer unit. However, the term is not intended to include thermoelastic ethylene interpolymers which are, in general, random polymers. Preferred block copolymers contain hard segments of styrenic type polymers in combination with saturated or unsaturated rubber monomer segments. Suitable block copolymers having unsaturated rubber monomer units include, but are not limited to, styrene-butadiene (SB), styrene-isoprene (SI), styrene-butadiene-styrene block copolymers (SBS), styrene-isoprene-styrene (SIS), ac-methylstyrene-butadiene-xcex1-methylstyrene or xcex1-methylstyrene-isoprene-xcex1-methylstyrene. The styrenic portion of the block copolymer is preferably a polymer or interpolymer of styrene and its analogs and homologs including xcex1-methylstyrene and ring-substituted styrenes, particularly ring-methylated styrenes.
Other preferred additional, optional polymers are homopolymers or interpolymers of aliphatic xcex1-olefins having from 2 to 20, preferably 2 to 18, more preferably 2 to 12, carbon atoms or xcex1-olefins having from 2 to 20, preferably 2 to 18, more preferably 2 to 12, carbon atoms and containing polar groups.
Suitable aliphatic xcex1-olefin monomers which introduce polar groups into the polymer include, for example, ethylenically unsaturated nitriles such as acrylonitrile, methacrylonitrile or ethacrylonitrile; ethylenically unsaturated anhydrides such as maleic anhydride; ethylenically unsaturated amides such as acrylamide or methacrylamide; ethylenically unsaturated carboxylic acids (both mono- and difunctional) such as acrylic acid or methacrylic acid; esters (especially lower, e.g. C1-C6, alkyl esters) of ethylenically unsaturated carboxylic acids such as methyl methacrylate, ethyl acrylate, hydroxyethylacrylate, n-butyl acrylate or methacrylate, 2-ethyl-hexylacrylate, glycidyl acrylate or glycidyl methacrylate; ethylenically unsaturated dicarboxylic acid imides, such as N-alkyl or N-aryl maleimides, such as N-phenyl maleimide. Preferably such monomers containing polar groups are acrylic acid, maleic anhydride and acrylonitrile. Halogen groups that can be included in the polymers with aliphatic c-olefin monomers include fluorine, chlorine and bromine; preferably such polymers are chlorinated polyethylenes (CPEs) or polyvinyl chloride.
Preferred are chlorinated polyethylenes, ethylene/methyl methacrylate polymers, ethylene/acrylic acid copolymers or polyvinylchlorides.
Suitable examples of homopolymers or interpolymers of aliphatic xcex1-olefins having from 2 to 20 carbon atoms are homopolymers of ethylene or propylene, such as isotactic polypropylene, and interpolymers of ethylene and one or more xcex1-olefins having from 3 to 8 carbon atoms, such as ethylene-propylene interpolymers, ethylene-1-octene interpolymers, propylene-ethylene random interpolymers; interpolymers of propylene and at least one xcex1-olefin containing from 4 to about 8 carbon atoms, terpolymers of ethylene, propylene and a diene, or rubber-toughened polypropylene. Preferred comonomers include 1-butene, 4-methyl-1-pentene, 1-hexene, and 1-octene. The olefinic polymer may also contain, in addition to the xcex1-olefin, one or more non-aromatic monomers interpolymerizable therewith, such as C4-C20 dienes, preferably butadiene or 5 ethylidene-2-norbornene.
Classes of useful olefinic polymers are generally long chain branched low density polyethylenes (LDPE), homogeneous or heterogeneous linear low density polyethylenes (LLDPE), linear high density polyethylenes (HDPE) or substantially linear olefin polymers (SLOP), as disclosed in U.S. Pat. Nos. 5,380,810; 5,272,236 and 5,278,272. Their melt index 12 according to ASTM D 1238 Procedure A, condition E, preferably is from 0.05 to 100 g/10 min., more preferably from 0.1 to 50 g/10 min., most preferably from 1 to 20 g/10 min. The olefinic polymers may be grafted.
The polymer composition of the present invention further comprises a foaming agent which is effective to render the composition foamable. Useful blowing agents include decomposable chemical blowing agents. Such chemical blowing agents decompose at elevated temperatures to form gases or vapors to blow the polymer composition into foam form. The agent preferably takes a solid form so it may be easily dry-blended with the polymer material. Chemical blowing agents include azodicarbonamide, azodiisobutyro-nitrile, benzenesulfonhydrazide, 4,4-oxybenzene sulfonyl-semicarbazide, p-toluene sulfonyl semi-carbazide, barium azodicarboxylate, N,Nxe2x80x2-dimethyl-N,Nxe2x80x2-dinitrosoterephthalamide, N,Nxe2x80x2-dinitrosopentamethylenetetramine, 4xe2x80x944-oxybis (benzenesulfonylhydrazide), trihydrazino triazine, sodium bicarbonate and citric acid. Azodicarbonamide is preferred. Additional teachings to chemical blowing agents are seen in F. A. Shutov, xe2x80x9cPolyolefin Foamxe2x80x9d, Handbook of Polymer Foams and Technology, pp. 382-402, D. Klemper and K. C Frisch, Hanser Publishers, Munich, Vienna, New York, Barcelona (1991). The chemical blowing agent is preferably blended with the polymer material in an amount sufficient to evolve 0.2 to 5.0, preferably from 0.5 to 3.0, and most preferably from 1.0 to 2.50 moles of gas or vapor per kilogram of polymer.
In some processes for making the present foam, a physical blowing agent may be used. Physical blowing agents include organic and inorganic agents. Suitable inorganic blowing agents include carbon dioxide, nitrogen, argon, water, air, nitrogen, and helium. Organic blowing agents include aliphatic hydrocarbons having 1-9 atoms, aliphatic alcohols having 1-3 carbon atoms, and fully and partially halogenated aliphatic hydrocarbons having 1-4 carbon atoms. Aliphatic hydrocarbons include methane, ethane, propane, n-butane, isobutane, n-pentane, isopentane, and neopentane. Aliphatic alcohols include methanol, ethanol, n-propanol, and isopropanol. Fully and partially halogenated aliphatic hydrocarbons include fluorocarbons, chlorocarbons, and chlorofluorocarbons. Examples of fluorocarbons include methyl fluoride, perfluoromethane, ethyl fluoride, 1,1-difluoroethane (HFC-152a), 1,1,1-trifluoroethane (HFC-143a), 1,1,1,2-tetrafluoro-ethane (HFC-134a), pentafluoroethane, difluoromethane, perfluoroethane, 2,2-difluoropropane, 1,1,1-trifluoropropane, perfluoropropane, dichloropropane, difluoropropane, perfluorobutane, perfluorocyclobutane. Partially halogenated chlorocarbons and chlorofluorocarbons for use in this invention include methyl chloride, methylene chloride, ethyl chloride, 1,1,1-trichloroethane, 1,1-dichloro-1-fluoroethane (HCFC-141b), 1-chloro-1,1-difluoroethane (HCFC-142b), chlorodifluoromethane (HCFC-22), 1,1-dichloro-2,2,2-trifluoroethane (HCFC-123) and 1-chloro-1,2,2,2-tetrafluoroethane (HCFC-124). Fully halogenated chlorofluorocarbons include trichloromonofluoromethane (CFC-11), dichlorodifluoromethane (CFC-12), trichlorotrifluoroethane (CFC-113), 1,1,1-trifluoroethane, pentafluoroethane, dichlorotetrafluoroethane (CFC-114), chloroheptafluoropropane, and dichlorohexafluoropropane. The amount of blowing agent incorporated into the polymer melt material to make a foam-forming polymer gel is preferably from 0.2 to 5.0, more preferably from 0.5 to 3.0, and most preferably from 1.0 to 2.50 moles per kilogram of polymer.
In addition, a nucleating agent may be added in the polymer composition in order to control the size of foam cells. Preferred nucleating agents include inorganic substances such as calcium carbonate, talc, clay, titanium oxide, silica, barium sulfate, diatomaceous earth or mixtures of citric acid and sodium bicarbonate, and the like. The amount of nucleating agent employed typically ranges from 0.01 to 5 parts by weight per hundred parts by weight of a polymer resin.
A stability control agent may be added to enhance dimensional stability of the present foam. Preferred agents include amides and esters of C10-24 fatty acids. Such agents are seen in U.S. Pat. Nos. 3,644,230 and 4,214,054, which are incorporated herein by reference. Most preferred agents include stearyl stearamide, glycerol monostearate, and sorbitol monostearate. Typically, such stability control agents are employed in an amount ranging from 0.1 to 10 parts per hundred parts of the polymer.
The polymer composition of the present invention may further contain a cross-linking agent. Possible cross-linking agents include peroxides, azides, silanes, phenols, sulfur-containing compounds, such as dithiocarbamates; thiazoles, imidazoles, sulfenamides and thiuramidisulfides; aldehyde-amine reaction products, ureas, guanidines; xanthates; paraquinonedioxime; dibenzoparaquinonedioxime, and combinations thereof. Such cross-linking agents are described in Encyclopedia of Chemical Technology, Vol. 17, 2nd edition, Interscience Publishers, 1968; and in Organic Peroxides, Daniel Seern, Vol. 1, Wiley-Interscience, 1970). In the case of substantially random interpolymers a1) not including an optional diene component, peroxide or azide cross-linking agents are preferred; in the case of interpolymers a1) with a styrene content of more than 50 weight percent azide cross-linking agents are preferred; and in the case of interpolymers a1) including an optional diene component sulfur-based and phenolic cross-linking agents are preferred.
Examples of useful organic peroxides include dicumyl peroxide, t-butylisopropylidene peroxybenzene, 1,,-di-t-butyl peroxy-3,3,5-trimethylcyclohexane, 2,5dimethyl-2,5-di(t-butyl peroxy) hexane, t-butyl-cumyl peroxide, di-t-butyl peroxide, and 2,5-dimethyl-2,5-di-(t-butyl peroxy) hexyne. Dicumyl peroxide and di-(tert-butylperoxy) di isopropyl benzene are preferred. Additional teachings regarding organic peroxide cross-linking agents are available in the Handbook of Polyme, Foams and Technology, pp. 198-204, supra. Suitable azides include azidoformates, such as tetramethylenebis(azidoformate); aromatic polyazides, such as 4,4xe2x80x2-diphenylmethane diazide; and sulfonazides, such as p,pxe2x80x2-oxybis(benzene sulfonyl azide). Suitable silanes include unsaturated silanes that comprise an ethylenically unsaturated hydrocarbyl group, such as a vinyl, allyl, isopropenyl, butenyl, cyclohexenyl or xcex3-(meth)acryloxy allyl group, and a hydrolyzable group, such as, for example, a hydrocarbyloxy, hydrocarbonyloxy, or hydrocarbylamino group.
The preferred gel level is at least 40% percent, more preferably at least 50% percent, most preferably at least 80% percent, based on the total weight of the polymers in the composition. Cross-linking agents may be added pure or in the form of a concentrate. The active component of the cross-linking agent employed to reach this gel level is generally at least 0.1 percent, typically at least 0.25 percent, often at least 0.5 percent, and generally up to 10 percent, preferably up to 6 percent, more preferably up to 3 percent, based on the total weight of the polymers in the composition.
Cross-linking may be promoted with a catalyst, such as organic bases, carboxylic acids, and organometallic compounds including organic titanates and complexes or carboxylates of lead, cobalt, iron, nickel, zinc and tin.
Rather than employing a chemical cross-linking agent, cross-linking may be effected by use of radiation. Useful radiation types include electron beam or beta ray, gamma rays, X-rays, or neutron rays. Radiation is believed to effect cross-linking by generating polymer radicals which may combine and cross-link. Additional teachings concerning radiation cross-linking are seen in C. P. Park, xe2x80x9cPolyolefin Foamxe2x80x9d Chapter 9, Handbook of Polymer Foams and Technology, D. Klempner and K. C. Frisch, eds., Hanser Publishers, New York (1991), pages 198-204, which is incorporated herein by reference.
The polymer composition may contain one or more further additives, for example inorganic fillers, antioxidants, colorants, pigments, light stabilizers, optical whitening agents, acid scavengers, ultraviolet absorbers, plasticizers, processing aids, ignition resistant additives, viscosity modifiers, antistatic additives or extrusion aids in known amounts.
The present foamable polymer composition may be prepared by blending one or more interpolymers a1) and/or a2) and optional polymer component(s) with one or more polydiorganosiloxanes b), one or more foaming agents c) and optional additives, in any suitable mixing device. The mixing temperature generally is from 80xc2x0 C. to 230xc2x0 C., preferably from 100xc2x0 C. to 200xc2x0 C., more preferably from 130xc2x0 C. to 180xc2x0 C. The interpolymer a1) and/or a2) and the polydiorganosiloxane b) and optional polymer component(s) can be directly combined in such an amount to produce a composition which preferably comprises from about 0.01 to about 20 weight percent, more preferably from about 0.1 to about 10 weight percent, and most preferably from about 0.5 to about 5 weight percent of one or more polydiorganosiloxanes b), based on the total weight of the polymers in the composition. Alternatively, a concentrate (masterbatch) of the polydiorganosiloxane b) in the above-described interpolymer a1) or a2) or in another thermoplastic polymer, such as the above-described low density polyethylene (LDPE), can be prepared and subsequently diluted with the interpolymer a1) and/or a2). The concentrates preferably comprise from 5 to 70 weight percent, more preferably from 25 to 60 weight percent of the polydiorganosiloxane b), based on the total weight of the concentrate. Once the components are relatively homogeneously dispersed within the polymer, the resulting mix is processed to foam. Useful processing temperatures generally are from 120xc2x0 C. to 250xc2x0 C., preferably from 150xc2x0 C. to 230xc2x0 C., more preferably from 160xc2x0 C. to 210xc2x0 C.
The foam structure which is prepared from the foamable polymer composition of the present invention may take any physical configuration known in the art, such as sheet, plank, injection molded articles, or foam slab stock. Other useful forms are expandable or foamable particles, moldable foam particles, or beads, and articles formed by expansion and/or coalescing and welding of those particles. Foams which are at a least partially cross-linked are preferred. The most preferred foams are injection-molded, cross-linked foams. The foam is particularly useful as a footwear component.
Excellent teachings to processes for making foam structures and processing them are seen in C. P. Park, xe2x80x9cPolyolefin Foamxe2x80x9d, Chapter 9, Handbook of Polymer Foams and Technology, edited by D. Klempner and K. C. Frisch, Hanser Publishers, Munich, Vienna, New York, Barcelona (1991).
In one embodiment of this invention, the foamable polymer blend comprising a decomposable chemical blowing agent and optionally a cross-linking agent is prepared and extruded through a die, optional cross-linking is induced and the extruded melt polymer material is exposed to an elevated temperature to release the blowing agent to form the foam structure. The polymer material and the chemical blowing agent may be mixed and melt blended by any means known in the art such as with an extruder, mixer, or blender. The chemical blowing agent is preferably dry-blended with the polymer material prior to heating the polymer material to a melt form, but may also be added when the polymer material is in melt phase. Cross-linking may be induced by addition of a cross-linking agent or by radiation. Induction of cross-linking and exposure to an elevated temperature to effect foaming or expansion may occur simultaneously or sequentially. If a cross-linking agent is used, it is incorporated into the polymer material in the same manner as the chemical blowing agent. Further, if a cross-linking agent is used, the foamable melt polymer material is heated or exposed to a temperature of preferably less than 150xc2x0 C. to prevent decomposition of the cross-linking agent or the blowing agent and to prevent premature cross-linking. If radiation cross-linking is used, the foamable melt polymer material is heated or exposed to a temperature of preferably less than 160xc2x0 C. to prevent decomposition of the blowing agent. The foamable melt polymer material is extruded or conveyed through a die of desired shape to form a foamable structure. The foamable structure is then cross-linked and expanded at an elevated or high temperature, typically, from 150xc2x0 C. to 250xc2x0 C. to form a foam structure. If radiation cross-linking is used, the foamable structure is irradiated to cross-link the polymer material, which is then expanded at the elevated temperature as described above.
A preferred method is the production of foamed molded parts by injection molding. Alternatively, the foamable melt polymer material can be coated onto a substrate, such as a fabric by calendering at a temperature below that required for foaming the polymer melt; and the coated substrate can be foamed at the foaming temperature or higher.
The present foamable polymer composition may also be formed into optionally cross-linked foam beads suitable for molding into articles. To make the foam beads, discrete resin particles such as granulated resin pellets are suspended in a liquid medium in which they are substantially insoluble such as water; impregnated with a blowing agent and optionally a cross-linking agent at an elevated pressure and temperature in an autoclave or other pressure vessel; and rapidly discharged into the atmosphere or a region of reduced pressure to expand to form the foam beads. A version is that the polymer beads are impregnated with blowing agent, cooled down, discharged from the vessel, and then expanded by heating or with steam. Blowing agent may be impregnated into the resin pellets while in suspension or, alternately, in non-hydrous state. The expandable beads are then expanded by heating with steam and molded by the conventional molding method for the expandable foam beads.
The foam beads may then be molded by any means known in the art, such as charging the foam beads to the mold, compressing the mold to compress the beads, and heating the beads to effect coalescing and welding of the beads to form the article. Optionally, the beads may be pre-heated with air or other blowing agent prior to charging to the mold.
The foam beads can also be prepared by preparing the foamable polymer composition, form the mixture into pellets, and heat the pellets to expand and optionally cross-link.
The density of the produced foam preferably is from 100 to 700 kg/m3, more preferably from 200 to 600 kg/m3, most preferably from 250 to 500 kg/m3.
The foamable polymer compositions of the present invention may be used for making foamed fabricated articles requiring good wear resistant properties, such coated fabrics, artificial leather, wire and cable, wheels for bicycles, wheel chairs and strollers, and particularly for producing footwear, especially shoe soles. When the fabricated article is a laminate, the layer comprising the polymer composition of the present invention is generally applied on the outer surface of the laminate.
By incorporating an above-described polydiorganosiloxane b) into the foam, the abrasion resistance of such foam can be significantly improved. The abrasion, measured according to the DIN 53516 test method, of the foam of the present invention incorporating the polydiorganosiloxane b) is generally at least 20 percent smaller, preferably at least 35 percent smaller, more preferably at least 50 percent smaller than that of a comparable foam not including the polydiorganosiloxane b). It has been surprisingly found that such increase in abrasion resistance is generally achieved without reduction of the coefficient of friction in grip tests under dry and/or wet conditions. It has even more surprisingly been found that in the preferred embodiments of the present invention the coefficient of friction of the foam incorporating the polydiorganosiloxane b) is even higher in grip tests under dry and/or wet conditions than a comparable foam which does not comprise a polydiorganosiloxane b).
It has also been found that the polymer composition of the present invention is highly suitable for injection molding and cross-linking processes. It has been found that the polymer composition of the present invention displays reduced sticking to molds, requiring a significantly reduced amount of mold release agents, and hence yielding a significantly reduced number of parts with insufficient quality.
The following examples are provided to illustrate the present invention. The examples are not intended to limit the scope of the present invention and they should not be so interpreted. Amounts are in weight parts or weight percentages unless otherwise indicated.